"Restrained Eating" May Put Bones at Risk

By Marcia Wood
April 6, 1999

WASHINGTON, April 6--Women who consistently limit what they eat to avoid gaining weight may undermine the health of their bones, Agricultural Research Service Administrator Floyd P. Horn said.

"Investigations into the role of nutrition in bone growth and maintenance are a priority of ARS' human nutrition research program," he said. "Now, a study by ARS researchers indicates that women may increase their risk of osteoporosis if they overemphasize being slim at the expense of good nutrition." ARS is the chief scientific agency of the U.S. Department of Agriculture.

Osteoporosis, a thinning and weakening of bone, increases the risk of fractures, particularly of the hip and spine. "The estimated annual costs of osteoporosis are more than $10 billion for care alone," said Horn. "But exercising and eating a well-balanced diet with adequate calcium are two of the best ways to keep bones strong and healthy."

Scientists with USDA's Agricultural Research Service in California looked at the eating behavior of 192 women volunteers between the ages of 18 and 50. Those classified as "restrained eaters" had significantly lower bone mineral content and bone mineral density than those who were classified as "normal eaters," said Horn.

"Data from the study show that women who are concerned about their weight, and thus restrain their eating, may increase their chances of developing osteoporosis," said physiologist Marta D. Van Loan with the ARS Western Human Nutrition Research Center at Davis.

"These restrained eaters," said Van Loan, "may be trying to meet a target weight that they've imposed upon themselves or that they think our image-conscious society demands." Van Loan and ARS chemist Nancy L. Keim conducted the study.

Scientists already know that not getting enough foods with calcium or other bone enhancing nutrients can lead to a low bone-mineral-density. But the California study, according to Van Loan, is apparently the largest of its kind to demonstrate a significant association between restricted eating and either bone mineral content or bone mineral density.

"Our volunteers were healthy individuals who did not have eating disorders such as bulimia or anorexia," Van Loan pointed out. "The majority of the volunteers, that is, 51 percent," said Van Loan, "can be classified as 'restrained eaters.' If this sample is representative of the U.S. female population as a whole, it means that one woman out of every two could potentially have this eating behavior, and may be increasing her risk of developing osteoporosis. It also means the number of women at risk of developing osteoporosis in the next 10 to 20 years could be greater than previous estimates."

Van Loan and Keim used a device called a DEXA, or dual energy x-ray absorptiometer, to measure bone mineral content and density. Those two factors are key indicators of overall bone strength and health, according to the scientists.

The researchers administered a standard test known as a Three-Factor Eating Inventory to determine if volunteers were always overly concerned about their weight, as is typical of restrained eaters.

Based on scores from the Three-Factor Inventory, Van Loan and Keim classified the women as "restrained eaters" or "normal eaters." The restrained eaters had about 12 percent less mineral content in their bones and about 6 percent lower bone mineral density than women with normal eating behavior, the researchers reported.

Foods that are a good source of calcium include cheese, milk, ice cream, most dark- green leafy vegetables, broccoli, baked beans and other dried legumes, dried figs and soft fish bones like those in canned salmon.

In addition to a diet rich in calcium, Keim said, proper exercise can help keep bones from becoming brittle and porous, especially exercise that "increases the force or load on your skeleton, such as jogging, lifting weights or working out with resistance-type gym equipment."

An article about the research appears in the April 1999 issue of the agency's monthly journal, Agricultural Research, and on the World Wide Web at:

/is/AR/archive/apr99/bone0499.htm

Scientific contact: Marta D. Van Loan and Nancy L. Keim, ARS Western Human Nutrition Research Center, c/o University of California at Davis, Davis, CA; phone (530) 752-4160 (Van Loan), (530) 752-4163 (Keim), mvanloan@whnrc.usda.gov or nkeim@whnrc.usda.gov.